1. Field of the Invention
The present invention relates generally to medical methods and systems. More particularly, the present invention relates to a method and driver for the controlled, reversible drilling of an occlusion in a body lumen, such as a calcific occlusion in a blood vessel.
Cardiovascular disease frequently arises from the accumulation of atheromatous material on the inner walls of vascular lumens, particularly arterial lumens of the coronary and other vasculature, resulting in a condition known as atherosclerosis. Atheromatous and other vascular deposits restrict blood flow and can cause ischemia which, in acute cases, can result in myocardial infarction or a heart attack. Atheromatous deposits can have widely varying properties, with some deposits being relatively soft and others being fibrous and/or calcified. In the latter case, the deposits are frequently referred to as plaque. Atherosclerosis occurs naturally as a result of aging, but may also be aggravated by factors such as diet, hypertension, heredity, vascular injury, and the like.
Atherosclerosis can be treated in a variety of ways, including drugs, bypass surgery, and a variety of catheter-based approaches which rely on intravascular widening or removal of the atheromatous or other material occluding the blood vessel. Particular catheter-based interventions include angioplasty, atherectomy, laser ablation, stenting, and the like. For the most part, the catheters used for these interventions must be introduced over a guidewire, and the guidewire must be placed across the lesion prior to catheter placement. Initial guidewire placement, however, can be difficult or impossible in tortuous regions of the vasculature. Moreover, crossing the occlusion with a guidewire is even more difficult if the lesion is total or near total, i.e. the lesion occludes the blood vessel lumen to such an extent that the lesion blocks advancement of the guidewire. Crossing the lesion is further exacerbated if the plaque is hardened or “calcific.”
To overcome this difficulty, forward-cutting atherectomy catheters have been proposed. Such catheters usually can have a forwardly disposed blade (U.S. Pat. No. 4,926,858) or rotating burr (U.S. Pat. No. 4,445,509). While effective in some cases, these catheter systems, even when being advanced through the body lumen with a separate guidewire, have great difficulty in traversing through the small and tortuous body lumens of the patients and reaching the target site.
As an improvement over forward cutting atherectomy catheters, the use of small guidewire-sized devices for crossing lesions has been proposed. Such devices can include a hypotube body or other relatively rigid shaft having a more flexible distal portion which is suitable for passing through small and tortuous regions of the vasculature and other body lumens. A very small drive shaft having a cutting element at its distal end is disposed in a lumen of the tubular body and extends from a distal end thereof. By rapidly rotating or rotationally oscillating the drive shaft, the cutting tip can penetrate even hardened, calcific occlusions. Such devices are described in detail in commonly owned U.S. Pat. Nos. 6,059,767 and 6,824,550, as well as co-pending application Ser. Nos. 10/950,161; 10/999,457; 11/146,483; 11/236,703; and 11/567,884, the full disclosures of which are incorporated herein by reference.
While very effective for crossing hardened lesions in the coronary and other vasculature, the rotating cutting tips can experience excessive friction and constriction when being advanced into the occlusion. The friction can come from the guidewire being advanced into the occlusion with excessive force, thus advancing the rotating tip too rapidly into the occlusion. Additionally, rotation of the tip can be limited by loose tissue wrapping around the tip. In either case, the constriction of the tip rotation can result in excessive torque being experienced by the drive shaft and motor. At a minimum, the excessive torque can hinder the performance of the guidewire and make advancement more difficult. More problematically, such excessive torque can damage the motor and/or fracture the guidewire shaft.
One solution to the problem of excessive torque in such cutting guidewires has been to employ rotational oscillation rather than unidirectional rotation of the cutting tip. Using a relatively high rotational speed, such as 12,000 rpm, and changing the rotational direction every 0.7 seconds, has been found to reduce but not eliminate the problems associated with constriction of the cutting tip as it is advanced through calcific and other lesions. Additionally, as described in commonly owned, co-pending application Ser. Nos. 11/388,251 and 11/636,388, the full disclosures of which are incorporated herein by reference, systems for rotationally oscillating drive shafts in cutting guidewires can be modified to monitor the load on the drive shaft and/or drive motor and to provide visual and/or audible feedback to the treating physician. The physician is alerted when the torque on the system approaches an unacceptable level so that the physician may pull back on the guidewire to relieve the constricting forces. While very effective and a significant advancement, changing rotational direction at a fixed interval does not optimize cutting efficiency.
For these reasons, it would be desirable to provide improved methods and systems for advancing cutting guidewires and other similar catheter systems through a body lumen. In particular, it would be desirable to provide methods and systems where control of a cutting tip of such guidewires and catheters is automatically adjusted in response to variations in the constrictive forces on the cutting tip as the guidewire or other catheter is advanced through occlusions in a body lumen. It would be particularly desirable if such automatic control of the cutting guidewire could be combined with the visual and audible feedback systems described above. At least some of these objectives will be met by the inventions described hereinbelow.
2. Description of Background Art
Exemplary cutting guidewire devices and control systems for providing visual and/or audible feedback on the level of torque experienced by the motors and drive shafts of such systems are described in the commonly owned patents and co-pending applications referenced above.